Process for separating olefins by adsorption

ABSTRACT

A method for the production of a solid adsorbent useful in the separation of olefins from a hydrocarbon feed mixture comprising olefins and paraffins and an olefin separation process employing the adsorbent so produced. The method basically comprises the steps of: contacting a base material comprising type X or type Y structured zeolite with a fluoride-containing solution of sodium hydroxide to effect the addition of alkali metal cations to and the extraction of alumina from the base material; washing the material at washing conditions until substantially free of sodium hydroxide; and drying the treated base material at conditions to reduce the LOI at 900* C. to less than about 10 wt. percent. The combination fluoride-caustic treatment produces a superior adsorbent for separating olefins from a hydrocarbon feed mixture comprising olefins and paraffins. The adsorbent produced has increased capacity for olefins, decreased catalytic activity and reduced dustiness. The process for separating olefins from a feed mixture comprising olefins and saturates comprises contacting at adsorption conditions the adsorbent so prepared with the feed mixture thereby selectively adsorbing the olefins.

United States Patent [191 Rosback June 10, 1975 PROCESS FOR SEPARATINGOLEFINS BY ADSORPTION [75] lnventor: Donald H. Rosback, Elmhurst, Ill.

[73] Assignee: Universal Oil Products Company, Des Plaines, 111.

221 Filed: May 17,1974

211 Appl. No.: 471,069

Related US. Application Data [62] Division of Ser. No. 401,782, Sept.28, 1973.

[52] US. Cl. 260/677 AD; 208/310; 252/455 Z Primary Examinerl-lerbertLevine Attorney, Agent, or FirmJames R. Hoatson, Jr.; Thomas K. McBride;William H. Page, 11

[5 7] ABSTRACT A method for the production of a solid adsorbent usefulin the separation of olefins from a hydrocarbon feed mixture comprisingolefins and paraffins and an olefin separation process employing theadsorbent so produced. The method basically comprises the steps of:contacting a base material comprising type X or type Y structuredzeolite with a fluoride-containing solution of sodium hydroxide toeffect the addition of alkali metal cations to and the extraction ofalumina from the base material; washing the material at washingconditions until substantially free of sodium hydroxide; and drying thetreated base material at conditions to reduce the LOI at 900 C. to lessthan about 10 wt. percent. The combination fluoride-caustic treatmentproduces a superior adsorbent for separating olefins from a hydrocarbonfeed mixture comprising olefins and paraffins. The adsorbent producedhas increased capacity for olefins, decreased catalytic activity andreduced dustiness. The process for separating olefins from a feedmixture comprising olefins and saturates comprises contacting atadsorption conditions the adsorbent so prepared with the feed mixturethereby selectively adsorbing the olefins.

6 Claims, No Drawings PROCESS FOR SEPARATING OLEFINS BY ADSORPTIONCROSS-REFERENCE TO RELATED APPLICATIONS This application is a divisionof my copending application Ser. No. 401,782 filed on Sept. 28, 1973.

BACKGROUND OF THE INVENTION 1. Field of the Invention The fields of artto which this invention pertain are crystalline aluminosilicateproduction and separation of hydrocarbon types with a crystallinealuminosilicate adsorbent. More specifically, this invention relatesboth to a method of modifying the characteristics of a base materialcomprising type X or type Y zeolite to produce an adsorbent havingcharacteristics desirable in a process for separating olefins from ahydrocarbon feed mixture containing olefins and to a separation processemploying this adsorbent to separate olefins from such a feed mixture.

2. Description of the Prior Art There are numerous methods for themanufacture and ion-exchange of various crystalline aluminosilicates,particularly the type X and type Y crystalline aluminosilicates, toyield products useful for effecting given hydrocarbon reactions orseparations. In the method of this invention, a manufacturing method hasbeen discovered whereby an adsorbent material is produced havingsuperior properties for the separation of olefins from a feed mixturecomprising olefins and paraffins.

A common problem encountered with most adsorbents and many catalysts isdust which can form excessive pressure drop after the adsorbent orcatalyst has been loaded into the adsorbent chambers or reaction vessel.Certainly it is for this reason that adsorbents and catalysts aremanufactured to meet certain minimum physical strength requirements andthat they are loaded into chambers and vessels with care to avoidbreakage. Although operations such as screening can be used to removemost of the interstitial smaller particles and dust, such operationsgenerally fail to remove dust which may coat particles of adsorbent orcatalyst of the proper size. This type of dust, apparently held to theparticle by electrostatic attraction, may then later be removed byliquid passing through the adsorbent chamber or catalyst vessel andaccumulate to form excessive pressure drops.

I have discovered that the troublesome dustiness characteristic ofadsorbents is virtually eliminated by a fluoride treatment of the basematerial. It is thought that the fluoride solublizes the dust byreacting with combined aluminum compounds present in the dust therebyremoving the dust from the particles.

A particular problem often encountered when using an adsorbent toseparate olefins from a hydrocarbon feed mixture is that the adsorbenttends to catalyze isomerization and polymerization of the feed olefins.Polymer produced blocks the pores of the adsorbent thereby reducing theeffectiveness of the adsorbent.

In the method of my invention I have additionally found thation-exchanging of a base material comprising type X or type Y zeolitewith a fluoride-containing aqueous solution of sodium hydroxide followedby washing at washing conditions until substantially free of sodiumhydroxide and drying at drying conditions'to reduce the volatile contentproduces an adsorbent with increased capacity for olefins and decreasedcatalytic activity. Furthermore, we have found that catalytic activityof the finished adsorbent decreased in proportion to the amount of thecation added to the zeolite by the caustic treatment. The cation addedby the ion exchange apparently replaces acid sites within the zeolitethat catalyze isomerization and polymerization reactions.

By the method of my invention therefore an adsorbent especially suitedfor olefin separation is produced having both increased capacity forolefins and decreased catalytic activity as well as reduced dustiness.The adsorbent produced is more efficient for use in an olefin separationprocess because of this increased capacity. Additionally, the adsorbenthas a longer effective life in the olefin separation process because ofits reduced catalytic activity and reduced dustiness.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a method for the manufacture of a zeolitic adsorbent whichmethod employs a type X or type Y structured zeolite as an intregalcomponent of the finished adsorbent. It is another object of the presentinvention to provide a method for the manufacture of an adsorbent whichhas superior properties when used in a process for the separation ofolefins from a hydrocarbon feed mixture. It is a further object of thisinvention to provide an improved process employing the adsorbent soproduced for the separation of olefins from a hydrocarbon feed mixture.

In brief summary, my invention is, in one embodiment, a method ofmanufacturing a solid adsorbent useful for the separation of olefinsfrom a feed mixture comprising olefins and paraffins which methodcomprises the steps of: (a) contacting a base material containing type Xor type Y zeolite with a fluoridecontaining solution of sodium hydroxidesolution at ion-exchange conditions to effect the addition of sodiumcations to and the extraction of alumina from the base material; (b)washing the ion-exchanged material at ion-exchange conditions untilsubstantially free of sodium hydroxide; and (c) drying the resultingexchanged mass at drying conditions to reduce the LOI at 900 C. to lessthan about 10 wt. percent.

In another embodiment, my invention is a process fo separating olefinsfrom a feed mixture comprising olefins and saturates which processcomprises contacting said mixture with an adsorbent prepared by steps(a), (b) and (c) above thereby selectively adsorbing at adsorptionconditions said olefins.

Other embodiments and objects of the present invention encompass furtherdetails such as operating conditions of various steps of the method allof which are hereinafter disclosed in the following discussion of eachof these facets of the invention.

DESCRIPTION OF THE INVENTION The type X and type Y crystallinealuminosilicates or zeolites herein contemplated are described as athreedimensional network of fundamental structural units consisting ofsilicon-centered SiO and aluminumcentered A10 tetrahedra interconnectedby a mutual sharing of apical oxygen-atoms. The space between thetetrahedra is occupied by water molecules and subsequent dehydration orpartial dehydration results in a 3 crystal structure interlaced withchannels of molecular dimension.

The type X structured and type Y structured zeolites as used in thisspecification shall include crystalline aluminosilicates having suchthree dimensional interconnected structures and as specifically definedby US. Pat. Nos. 2,882,244 and 3,130,007. The term type X structured andtype Y structured zeolites shall include all zeolites which have ageneral structure as represented in the above cited patents.

Thetype X structured zeolite in the hydrated or partially hydrated formhas the general empirical formula as shown in Formula 1 below:

where M represents at least one cation having a valence of not more than3, n represents the valence of M and y is a value up to about 8depending upon the identity of M and the degree of hydration of thecrystal. The cation M may be one or more of a number of cations such asthe hydrogen cation, the alkali metal cations, or the alkaline earthcations or other selected cations and is generally referred to as anexchangeable site.

The type Y structured zeolite in the hydrated or partially hydrated formcan be represented in terms of the mole oxides for the sodium form asrepresented by F ormula 2 below:

FORMULA 2 (0.9:02 )Na O:Al O :wSiO :yl-l O where w is a value of greaterthan about 3 up to 8, and y may be any value up to about 9.

The term type X zeolite" and type Y zeolite as employed herein shallrefer not only to type X structured and type Y structured zeolitescontaining sodium cations but to those containing other cations such asthe hydrogen cations, the alkali metal cations, or the alkaline earthcations. Typically both the type X and type Y structured zeolites asinitially prepared are predominantly in the sodium form but they maycontain, possibly as impurities, the other cations as mentioned above.

The term base material as used herein shall refer to a type X or type Yzeolite-containing starting material used to make the final adsorbent bythe method of this invention. Usually such base material will bepredominantly in the sodium form of the zeolite. Generally the basematerial will be in the form of particles such as extrudates,aggregates, tablets, pills, macro-spheres, or granules produced bygrinding any of the above to a desired size range. The type X and type Yzeolite can be present in the base material in concentrations generallyranging from about 75 wt. percent to about 90 wt. percent of the basematerial based on a volatile free composition. The remaining material inthe base material generally comprises amorphous silica or alumina orboth which is present in intimate mixture with the zeolite material.This amorphous material may be an adjunct of the manufacturing processof the type X or type Y zeolite (for example, intentionally incompletepurification of the zeolite during its manufacture) or it may be addedto the relatively pure zeolite to aid in forming particles of thezeolite.

A specific base material is commercially available nominal l 16-inchextrudate comprising 13X zeolite and a minor amount of amorphousmaterial as binder. This base material is primarily in the sodium form;that is, the cation represented as M in Formula 1 above is primarilysodium. By chemical analysis the Na O/Al O ratio is usually about 0.7 orless and can typically be about 0.6 or less which, it should be noted,is less than the 0.9102 indicated in Formula l above. Other cations suchas H+ and any of the Group A metal cations may be present, primarily asimpurities, to supply the remainder of the cations needed for chemicalbalance. The silica to alumina ratio of this starting material by X-raydetermination is about 2.5 and the same ratio by chemical analysis isabout 2.6. Normally the starting material whether in the extrudate orpellet form is granulated to a particular size range of about 2040 mesh(U.S. Standard Mesh) before the first ion exchange step is begun. Thisis approximately the desired particle size of the finished adsorbent.

The treatment step with a fluoride-containing sodium hydroxide solutionis primarily an ion exchange step in which sodium cations replacenon-sodium cation impurities in the zeolite-containing base materialthereby essentially eliminating the catalytic activity of the zeolite.Although mild ion exchange conditions are employed, this stepadditionally removes a small amount of silica and alumina therebyincreasing the capacity of the material for olefins and essentiallyeliminating the dustiness characteristic of the final adsorbent. It isthought that the fluoride solubilizes the dust by reacting with combinedaluminum compounds present thereby removing the dust from the particles.Total silica and alumina removal from the precursor mass is from about Iup to about 15% and is generally in the range of l to 5 percent.Analyses indicate that the bulk of both soluble and insoluble materialremoved from the base material is aluminum, as alumina or sodiumaluminate. At least a portion of the alumina extracted appears to befrom the zeolite itself rather than from any amorphous material sincethere is some nominal loss of zeolite as detected by X-ray analysisafter this step. It is not known whether the small amount of silicaremoved from the base material came from the crystalline (zeolite)portion or the amorphous portion of the base material.

I have foundnot only that this ion exchange step significantly reducescatalytic activity but specifically that the amount of activityreduction is proportional to the amount of sodium cation contained bythe finished adsorbent. This relationship, with the amount of sodiumexpressed as the ratio Na O/Al O is indicated in Table 1 below.Catalytic activity, by a method hereinafter described, was determinedfor a base material comprising 13X zeolite and for various adsorbents,each having a different Na O/Al O ratio, prepared from the basematerial.

Table l-Continued Relationship Between Na O/Al O and Catalytic ActivityAs shown in the table, catalytic activity decreases with increasedsodium ion content from an unacceptable 55 dimer units of the startingmaterial which has a Na O/Al O ratio of about 0.6 to about zero dimerunits as the Na O/Al O- ratio approaches 1. For an acceptable adsorbentit is preferred that the Na O/AI O ratio of the final product be greaterthan about 0.70.

lon exchange conditions should be so regulated to achieve this desireddegree of ion exchange. The degree of ion exchange achieved is afunction of the three variables of caustic and fluoride concentrations,temperature at which the ion exchange is conducted, and the length oftime the ion exchange is continued.

The preferred fluoride-containing sodium hydroxide solution employedwill be sodium hydroxide and sodium fluoride dissolved in water.Suitable concentrations to obtain the desired ion exchange can be fromabout 0.5 to wt. percent of sodium hydroxide with the preferredconcentration being from about 0.5 to about 5 wt. percent and from about0.1 wt. percent up to the solubility limit (about 5 percent) of sodiumfluoride. By using solutions containing sodium hydroxide and sodiumfluoride within these ranges of concentrations, the desired ion exchangecan be obtained at temperatures from about 50 to 250 F. withtemperatures from about 150 to 250 F. being especially preferred.Operating pressure is not critical and need only be sufficient to insurea liquid phase. Operating pressures can range from about atmosphericpressure to about 100 psig. The length of time required for the ionexchange will vary, depending upon the solution concentration andtemperature, from about 0.5 to 5 hours. Within the above preferredconcentrations and temperature ranges a contact time which has beenshown to be especially preferred is about 2 to 3 hours. Continuous orbatch-type operations can be employed. The ion exchange step should becontrolled so that the zeolite structure will not be destroyed and sothat the final product will have a Na O/Al O ratio greater than about0.7.

The next step in the method of manufacture of this invention is thewashing step for the purpose of removing excess sodium hydroxidesolution remaining within the ion-exchanged base material. The washingmedium is water which has a pH within the range of 7 to 10 andpreferably within the range of 9 to 10. If necessary, the water isadjusted to and maintained within the desired pH range by adding smallquantities of acid or base. Since the primary purpose of the ionexchange was to remove hydrogen cation (and metal cation) contaminantswhich are thought to cause catalytic activity, this pH range isnecessary to avoid redepositing hydrogen cation on the adsorbent mass.Washing temperatures can include temperatures within the range of about50 F. to about 250 F. with a temperature of about 100 F. to 150 F.preferred. Although the washing step can be done in a batch manner withone aliquot of wash water at a time, the washing step can be done on acontinuous flow type basis with water passed through a bed of theadsorbent at a given liquid hourly space velocity and a temperature fora period of time in order that from about 1 to about 5 gallons of waterper pound of starting material is used to wash the material. Preferredcontinuous washing conditions include using liquid hourly spacevelocities from about 0.5 to about 5, with 1.5 being preferred, to passfrom about I to about 3 gallons of wash water per pound of startingmaterial over the ion exchanged adsorbent. A good indication of completewashing is made by measuring the pH of the effluent wash water andcomparing it to the pH of the fresh feed wash water. When they are thesame, washing can generally be considered as complete.

When the wash step is completed the wet adsorbent particles will usuallycontain from about 30 to about 50 wt. percent volatile matter (water) asmeasured by loss on ignition at 900 C. In this specification, thevolatile matter content of the zeolitic adsorbent is determined by theweight difference obtained before and after drying a sample of adsorbentin a high temperature furnace at 900 C. under an inert purge gas streamsuch as nitrogen for a period of time sufficient to achieve a constantweight. The difference in weight, calculated as a percentage of thesamples initial weight, is reported as loss on ignition (LOI) at 900 C.and represents the volatile matter present within the adsorbent. Theremaining step in the method of manufacture then is drying step toreduce the LOI at 900 C. to less than about 10 wt. percent with thepreferred LOI being about 3 to 7 wt. percent. After the washing has beencompleted, the particles are unloaded and dried in a force air oven attemperatures within the range of from about F. to about 1000 F. for aperiod of time sufficient to remove enough water so that the volatilematter content of the zeolite is below about 10 wt. percent. Othermethods of drying may be used which can include drying in the presenceof an inert gas or under a vacuum, or both.

Since the anticipated use for the adsorbent prepared by the method ofthis invention is in various processes for the separation of olefinichydrocarbons from a feed mixture containing olefinic and saturatedhydrocarbons, the particular usefulness of this adsorbent and generalinsight into its desirable characteristics may be better understood bybrief reference to those processes.

Charge stocks which may be charged to selective adsorption processesemploying the adsorbent produced by the method of my invention maycontain olefins in the C -C carbon range. Of these olefins, the C -Cnormal mono-olefins are generally produced by catalyticallydehydrogenating a C -C normal paraffin stream. The effluent stream froma dehydrogenation process generally contains about 5 to 25 percentolefins and may require further processing in order to concentrate thenormal olefinic hydrocarbons. A typical example of the composition ofthe effluent stream from a dehydrogenation process is shown below inTable 2:

TABLE 2 DEHYDROGENATION REACTOR EFFLUENT ANALYSIS BY GAS-LIQUIDCHROMATOGRAPHY TABLE 2-Continued DEHYDROGENATION REACTOR EFFLUENTANALYSIS BY GAS-LlQUlD CHROMATOGRAPHY n-C paraffins 27.8 n-C olefins 2.6n-C paraffins 22.6

n-C olefins 2.7 n-C paraffins l2.l n-C olefins l.7 n-C paraffins 0.4Total non-normals 3.3 TOTAL 100.0

Total normal olefins 8.8 Total normal paraffins 87.9 Total n-normals 3 3TOTAL 100.0

VOL.

Total olefins 9.8 Light ends 0.2 Total paraffins 86.5 Total non-normals3 5 TOTAL 100.0

The 3.5 volume percent non-normals in the above analysis are primarilyaromatics. Another possible charge stock for the process would be aselected fraction from a gasoline produced by a fluid catalytic crackingunit. A typical analysis, from a 95C. cut of such gasoline is asfollows:

. VOL. Olefins 25 .4 Paraffins and naphthenes 72.3 Aromatics 2 .3 TOTAL100.0

In separating the olefinic hydrocarbon from the feed mixture, the feedis contacted with a bed or beds of the adsorbent and the olefinichydrocarbons are selectively retained by the adsorbent while theunadsorbed or raffinate mixture comprising saturated hydrocarbons isremoved from the interstitial void spaces between the particles ofadsorbent and the surface of the solid adsorbent. The adsorbent may thenbe contacted with a desorbent material which is capable of displacingthe adsorbed olefinic hydrocarbons from the adsorbent.

The adsorbent can be contained in one or more chambers where throughprogrammed flow into and out of the chambers separation of the olefinichydrocarbons is effected. A particularly preferred process to use theadsorbent of my invention employs the simulated moving-bedcountercurrent operations similar to those disclosed in the pattern ofoperations in US. Pat. No. 2,985,589 and more specifically in U.S. Pat.No. 3,510,423.

The preferred process for separating olefins from a feed mixturecomprising olefins and saturates would comprise the steps of: contactingthe feed mixture with the adsorbent'at adsorption conditions to effectthe selective retention of the olefins by the adsorbent, withdrawingfrom the bed of adsorbent a raffinate stream comprising less selectivelyadsorbed feed mixture components, contacting the adsorbent with adesorbent material at desorption conditions to effect desorption of theolefins from the adsorbent, and withdrawing a stream containing theolefins and desorbent from the adsorbent. The longer useful life of myadsorbent would be an improvement to such processes as this one in whicha regeneration step is not included in the normal sequence ofoperations.

Preferred operating conditions of this particular pro- The adsorbentproduced by the method of this inven-' tion may of course be used inother selective adsorption processes for separating olefins. These mightinclude, for instance, swing-bed or moving bed process in which bothadsorption and desorption are conducted in the vapor phase or in whichone operation is conducted in the vapor phase and the other in theliquid phase. Operating pressures and temperatures for adsorption anddesorption might be the same or different.

The desorbents which can be used in processes employing this adsorbentwill vary depending on the type of operation employed. In the swing bedsystem in which the preferably adsorbed olefins are removed from theadsorbent by a purge stream, gaseous hydrocarbons or other type gasesmay be used at elevated temperatures or reduced pressures or both toeffectively purge adsorbed olefins from within the sorbent. However, inother type operations which are generally operated at substantiallyconstant pressures and temperatures, the desorbent relied upon must bejudi-' ciously selected in order that it may displace the preferredolefin adsorbed from the feed within the adsorbent without dulypreventing the feed olefins from displacing the desorbent in a followingadsorption cycle.

Desorbents which can be used in the olefin separation process of thisinvention should also be materials that are easily separable from thefeed mixture that is passed into the process. In desorbing thepreferentially adsorbed component of the feed both desorbent and thedesorbed feed component are removed from the adsorbent in admixture.Without a method of separation in these two materials, the purity of theselectively adsorbed component of the feed stock would not be very highsince it would be diluted with desorbent. It is contemplated that adesorbent having a different boiling range than the feed mixture shouldbe used in this process. The use of a desorbent of a different boilingrange allows a simple separation by fractionation 'or other methods toremove desired feed components from the desorbent and allow reuse of thedesorbent in the process. Specifically in processes employingsubstantially isothermal and isobaric liquid phase operations, it ispreferred to use a desorbent containing olefins or aromatics having aboiling range different than that of the feed 'mixture.

With the type of processes employing adsorbents to separate olefins nowin mind, one can appreciate that certain characteristics of adsorbentsare highly desir able, if not absolutely necessary, to the successfuloperation of the selective adsorptive process. Among suchcharacteristics are: adsorptive capacity for some volume of desiredolefins per volume of adsorbent; reduced or eliminated catalyticactivity for undesired side reactions such as polymerization andisomerization; and selectivity of adsorption both for the desired carbonnumber range of olefins. Low or no initial dustiness of the adsorbentand attrition resistance are equally important to avoid possiblepressure drop problems after the adsorbent has been loaded.

Capacity of the adsorbent for adsorbing a specific volume of olefins isof course a necessity; without such capacity the adsorbent is uselessfor adsorptive separation. Furthermore, the higher the adsorbentscapacity for the species to be adsorbed, the better is the adsorbent.Increased capacity of a particular adsorbent makes it possible to reducethe amount of adsorbent needed to separate the desired species containedin a particular rate of hydrocarbon feed mixture. A reduction in theamount of adsorbent required for a specific adsorptive separationreduces the cost of the separation process. It is important that thegood initial capacity of the adsorbent be maintained during actual usein the separation process over some economically desirable life.

For this reason, and others, it is necessary that the adsorbent possesslittle or no catalytic activity which would produce products that mightdegrade adsorbent capacity or selectivity. It is additionally importantthat the highly reactive olefins are not reacted into side productswhich either degrade the product quality or reduce the overall yield ofconcentrated olefins. In instances where the feed streams include bothnormal and isomeric olefin hydrocarbons which are to be separated andrecovered together as a single product stream, the isomerizationactivity of the adsorbent is not a great impediment to the processeconomics. Where, however, a specific olefin is desired as a productstream, isomerization activity of the adsorbent is a primeconsideration. In either case, a reduction of polymerization activity isvery important because of polymerization, in addition to reducing theyields of olefinic hydrocarbons also, as mentioned above, tends todegrade the adsorbent. The polymerization effects are generallyconsidered to be primarily physical impediments which can prevent theolefinic hydrocarbons from passing into the molecular sieve adsorbent byplugging up the surface of the adsorbent. This shortens the useful lifeof the adsorbent and makes necessary frequent regeneration treatments torestore the adsorptive properties of the adsorbent.

Since both reactions seem to occur at the same time, the term catalyticactivity as used herein shall mean both isomerization and polymerizationactivity. It is, therefore, extremely important that the catalyticactivity be substantially reduced or preferably totally eliminated byproper methods of manufacture of a selected adsorbent.

While reducing the temperature of the operations of the adsorptionprocess in which the catalytic activity is present will substantiallyreduce the catalytic activity because of the associated reduction in therate of reaction, this procedure in adsorptive separation processesemploying molecular sieves is, generally not desirable because thereduction in temperature also reduces the kinetic energy of thematerials passing into and out of the adsorbent. This substantiallyreduces the rate of exchange of feed olefins into and out of theadsorbent giving what is considered in the art as poor breakthroughfronts which result in product contamination with feed stock andrelatively high requirements of adsorbents for a given throughput ofolefincontaining feed stock.

The other important adsorbent characteristic is the ability of theadsorbent to separate components of the feed; or, in other words, theselectivity, (B), of the adsorbent for one component as compared toanother component. Selectivity is expressed not only for the desiredhydrocarbon type (olefins) as compared to undesired hydrocarbons but isalso expressed between homologs of the desired hydrocarbon type. Theselectivity (B) as used throughout this specification is defined as theratio of the two components of the adsorbed'phase over the ratio of thesame two components in the unadsorbed phase at equilibrium conditions.

Selectivity is shown as Equation 1 below:

Equation 1 I [vol. ercent C/vol. ercent D Selectivity (B) [vol. EercentC/vol. percent where C and D 'are two components of the feed representedin volume percent and the subscripts A and U represent the adsorbed andunadsorbed phase respectively. The equilibrium conditions as definedhere were determined when the feed passing over a bed of adsorbent didnot change composition after contacting the bed of adsorbent. In otherwords, there was no net transfer of material occurring between theunadsorbed and adsorbed phases.

As can be seen where the selectivity of two components approaches 1.0there is no preferential adsorption of one component by the adsorbent.As the (B) becomes less than or greater than 1.0 there is a preferentialselectivity by the adsorbent of one component. When comparing theselectivity by the adsorbent of one component C over component D, a (B)larger than 1.0 indicates preferential adsorption of component C withinthe adsorbent. A (B) less than 1.0 would indicate that component D ispreferentially adsorbed leaving an unadsorbed phase richer in componentC and an adsorbed phase richer in component D. Desorbents ideally wouldhave a selectivity equal to about 1 or slightly less than 1.

The remaining important characteristic, not only for adsorbents but forcatalysts as well, is low initial dustiness. This characteristic must ofcourse be coupled with sufficient particle mechanical strength to resistsubsequent dust formation during process usage. Such dust, whetherpresent initially or developed later, may migrate within the adsorbentchamber or reaction vessel during process use to form flow restrictionsfrom which excessive pressure drops can result. Such pressure dropsgrind up adsorbent or catalyst present in the chamber or vessel and canexceed equipment mechanical limitations thereby forcing prematureprocess shutdowns. I have discovered that the dustiness characteristicof adsorbents can be eliminated by a fluoride treatment step in themanufacture of such adsorbents. I would expect that such a step could beincorporated in catalyst manufacture procedures as well to eliminate thedustiness characteristic of any such catalyst.

The adsorbent produced by the method of this invention has good capacityand selectivity for olefins couj pled with essentially no catalyticactivity or dustiness characteristics or adsorptive capacity,selectlvity, and

degree of catalytic activity, a dynamic testing apparatus was employed.The apparatus used consisted of an adsorbent chamber of approximately 40cc. volume having inlet and outlet portions at opposite ends of thechamber. The chamber was contained within a temperature control meansand, in addition, pressure control equipment was used to operate thechamber at a constant predetermined pressure. Attached to the outletline of the chamber was chromatographic analysis equipment which wasused to analyze the effluent stream leaving the adsorbent chamber.

The actual operations of the pulse test used to determine the adsorbentcapacity were as follows: a feed mixture containing a tracer componentfor ease of chromatographic analysis and at least one adsorbablecomponent in a dilute component was passed through the adsorbent beduntil the effiuent stream leaving the adsorbent chamber, as measured bythe chromatograph, was essentially the same composition as the feedstream passing into the inlet of the sorbent chamber. Generally theadsorbable component used in the feed mixture was decene-l. Thisindicates that the sieve has reached equilibrium, that is, the adsorbentwas no longer adsorbing materials from the external phase and that therewas no longer a net transfer of the material between the adsorbed phaseand the external phase.

A desorbent mixture, containing a tracer component and an adsorbablecomponent different from that of the feed, in a diluent component, wasthen passed into the adsorbent chamber at conditions to effectdesorption of the previously adsorbed feed mixture component. Octene-lwas usually used as the adsorbable component in the desorbent mixture.The desorbent mixture was continuously passed into the adsorbent chamberuntil the effiuent material, as monitored by the chromatographicequipment was substantially identical to the desorbent feed material,indicating that equilibrium conditions has been achieved. Knowing theflow rate to the chamber and the effluent composition as continuouslymonitored by the chromatograph, the total amount of the componentsadsorbed by the adsorbent from the desorbent mixture can be calculated.

In order to determine the adsorptive capacity of the sieve forcomponents in the feed mixture, the inlet stream to the chamber was thenswitched from the desorbent mixture back to the feed mixture to allowfeed components to displace the previously adsorbed components from thedesorbent mixtures. Again using the traces developed by thechromatograph and knowing the flow rate, the volume of feed componentsadsorbed can be calculated.

Selectivity can then be calculated using the previously mentionedequation for selectivity and the capacities determined above.

In measuring the polymerization activity of the adsorbent, the same gaschromatographic equipment and testing apparatus was used. Two variationsof the polymerization test can be used. In the first variation, thedegree of catalytic activity may be measured by the loss of a knownconcentration of feed olefins as detected in the effiuent stream by thechromatographic equipment. The measure of polymerization is then anindirect determination, being related to the difference between theinlet and outlet olefin concentrations. This catalytic activity isthought to be primarily due to polymerization reactions of the feedolefins with a small part of the feed olefins that are isomerized toother internal olefinic isomers. The relative activity scale used toexpress the catalytic activity of the adsorbent is determined bymeasuring the peak height on the chromatograph equivalent to the inletconcentration of olefin as indicative of a zero catalytic activity.Hence, if the peak height of the olefins present in the effiuent is thesame as the peak height of a known concentration of olefins present inthe feed, the relative adsorbent activity is zero. An effiuent peakheight equal to one half that of the feed would represents exactly 50%polymerization or isomerization of the feed olefin component. Theadsorbent activity would therefore be 50%. Equation 2 below representsthe formula used to determine catalytic activity on an adsorbent knowingthe peak height of the olefins remaining in the effiuent stream leavingthe adsorbent chamber and the peak height of the olefins present in thefeed.

Equation 2 where Pe represents the peak height of the effluent olefinsand Pf represents the peak height of the feed olefins.

The second variation of catalytic activity test is to measure thepolymer formed directly in the effiuent stream with the chromatographicequipment. This method depends upon selecting a feed olefin, such asdi-isobutylene, that easily forms an identifiable polymer. The dimerpeak height above the base line is then used as the measure ofpolymerization and catalytic activity is reported as dimer units. Bothtest variations can be used with the second method being the moresensitive in determining catalytic activity.

A comparison of the dust content of adsorbents was made by simplypouring 10 ml. of the adsorbent into 40 ml. of methanol contained in a25 X mm 8 dram vial, mixing the contents, the observing or measuring theopacity of the methanol. The dust is dispersed in the alcohol and thedegree of opacity serves as an index of the dust content. A specificdust test involves adding 10 ml. of adsorbent to 40 ml. of methanol in avial and mixing the contents of the vial by rotation at 15 rpm. for 5minutes. A 10 ml. portion of liquid was then drawn off, diluted with 10ml. of fresh methanol and a sample was placed in a 1 ml. measurementcell. Optical density measured at 400 nanometers was then determined andthat determination served as an index of the adsorbents dust content.

Confirming pulse, catalytic activity and dust test data required testingof the adsorbent in a continuous countercurrent liquidsolid contactingdevice to determine the adsorbents actual performance in an olefinseparation process.

The general operating principles of such a device have been previouslydescribed and are found in Broughton US. Pat. No. 2,985,589 and aspecific laboratory-size apparatus utilizing these principles isdescribed in deRosset et al US. Pat. No. 3,706,812. The equipmentcomprises multiple adsorbent beds with a number of access lines attachedto distributors within the beds and terminating at a rotary distributingvalve. At a given valve position, feed and desorbent are beingintroduced through two of the lines and raffinate and extract arewithdrawn through two more. All remaining access lines are inactive andwhen the position of the distributing valve is advanced by one index allactive positions will be advanced by one bed. This simulates a conditionin which the adsorbent physically moves in a direction countercurrent tothe liquid flow. Additional details on adsorbent testing and evaluationmay be found in the paper Separation of C Aromatics by Adsorption by A.J. deRosset, R. W. Neuzil, D. J. Korous and D. H. Rosback presented atthe American Chemical Society, Los Angeles, California, Mar. 28, Apr. 2,1971.

The superior performance indicated by pulse test and activity test dataobtained on adsorbents prepared by the method of adsorbent preparationdescribed herein was confirmed by continuous testing in this device.Thus, also the olefin separation process described herein wassuccessfully demonstrated.

EXAMPLE In this example three adsorbents were prepared from the samebase material and tested to illustrate the desired properties achievedby the method of this invention.

The three adsorbents were prepared from base material comprisingcommercially available l3X zeolite in the form of nominal 1/16 X A; inchextrudate. This base material was ground to produce 20-40 U. S. StandardMesh particle size material and divided into three portions from whichthree adsorbents, A, B, and C, were prepared.

One portion of base material received no treatment with either sodiumhydroxide alone or in combination with sodium fluoride and was tested asAdsorbent A.

A second portion was treated with a dilute solution of NaOH only andthen water washed to produce Adsorbent B. A 200 cc. portion of the basematerial was batch treated for 2 hours at 90 C. with a solution of 20 g.NaOH dissolved in 500 ml. of deionized water. The material was thenwashed by decantation with five 500 ml. portions of water, two at 25 C.,three at 50 C.

A third portion was treated with a solution containing both NaF and NaOHand then water washed to produce Adsorbent C. A 200 cc. portion of thebase material was batch treated for 2 hours at 90 C. with a solution of25 g. NaF and 20 g. NaOH dissolved in 500 ml. of deionized water. Thematerial was batch washed in the manner described above.

All three adsorbents were dried for 16 hours at 185 C. with perfluent Nand then rehydrated to 4 wt. percent water prior to being tested forperformance by the pulse, activity and dustiness tests previouslydescribed.

The results of the testing for the three adsorbents are shown in Table 3below:

Table 3 Capacity and Dustiness Test Data for Adsorbents The higherolefin capacity shown for adsorbents B and C indicate that either theNaOH or the NaOH/NaF treatment increases olefin capacity. While the NaOHtreatment alone significantly reduces catalytic activity and dustiness,the combination NaOH and NaF essentially eliminates both catalyticactivity and dustiness. Thus the NaOH and NaF treatment produces anadsorbent with the best combination of characteristics.

I claim as my invention:

1. A process for separating olefins from a feed mixture comprisingolefins and saturates which process comprises contacting said mixturewith an adsorbent prepared by the steps of:

a. contacting a base material comprising type X or type Y zeolite with afluoride-containing aqueous sodium hydroxide solution at ion exchangeconditions to effect the addition of sodium cations and the extractionof alumina from said base material;

b. washing the sodium-exchanged base material at washing conditionsuntil essentially free of sodium hydroxide; and,

c. drying the material at conditions to reduce the LOl at 900 C. to lessthan about 10 wt. percent, thereby selectively adsorbing at adsorptionconditions said olefins.

2. The process of claim 1 further characterized in that said olefinshave from about 4 to 25 carbon atoms per molecule.

3. The process of claim 1 further characterized in that said adsorptionconditions are selected from a temperature within the range of fromabout F. to about 450 F. and a pressure within the range of from aboutatmospheric to about 500 psig. to maintain liquid phase.

4. A process for separating olefins from a feed mixture comprisingolefins and saturates which process comprises the steps of:

a. contacting said mixture with an adsorbent at adsorption conditions toeffect the selective adsorption of said olefins;

b. withdrawing from the adsorbent stream comprising less selectivelyadsorbed feed mixture components;

c. contacting the adsorbent with a desorbent material at desorptionconditions to effect desorption of olefins from the adsorbent; and,

d. withdrawing from the adsorbent a stream containing feed mixtureolefins and. desorbent;

wherein said adsorbent is prepared by the steps of:

i. contacting a base material comprising type X or type Y zeolite with afluoride-containing aqueous sodium hydroxide solution at ion exchangeconditions to effect the addition of sodium cations and the extractionof alumina from said base material;

ii. washing the sodium-exchanged base material at washing conditionsuntil essentially free of sodium hydroxide; and,

iii. drying the material at conditions to reduce the LOI at 900 C. toless than about 10 wt. percent.

5. The process of claim 4 further characterized in that said adsorptionand desorption conditions are selected from a temperature within therange of from about 70 F. to about 450 F. and a pressure within therange of from about atmospheric to about 500 psig. to maintain a liquidphase.

6. The process of claim 4 further characterized in that said olefinshave from about 4 to about 25 carbon atoms per molecule.

1. A PROCESS FOR SEPARATING OLEFINS FROM A FEED MIXTURE COMPRISINGOLEFINS AND SATURATES WHICH PROCESS COMPRISES CONTACTING SAID MIXTUREWITH AN ADSORBENT PREPARED BY THE STEPS OF: A. CONTACTING A BASEMATERIAL COMPRISING TYPE X OR TYPE Y ZEOLITE WITH A FLUORIDE-CONTAININGAQUEOUS SODIUM HYDROXIDE SOLUTION AT ION EXCHANGE CONDITIONS TO EFFECTTHE ADDITION OF SODIUM CATIONS AND THE EXTRACTION OF ALUMINA FROM SAIDBASE MATERIAL; B. WASHING THE SODIUM-EXCHANGED BASE MATERIAL AT WASHINGCONDITIONS UNTIL ESSENTIALLY FREE OF SODIUM HYDROXIDE; AND, C. DRYINGTHE MATERIAL AT CONDITIONS TO REDUCE THE LOI AT 900*C. TO LESS THANABOUT 10 WT. PERCENT, THEREBY SELECTIVELY ADSORBING AT ADSORPTIONCONDITIONS SAID OLEFINS.
 2. The process of claim 1 further characterizedin that said olefins have from about 4 to 25 carbon atoms per molecule.3. The process of claim 1 further characterized in that said adsorptionconditions are selected from a temperature within the range of fromabout 70* F. to about 450* F. and a pressure within the range of fromabout atmospheric to about 500 psig. to maintain liquid phase.
 4. Aprocess for separating olefins from a feed mixture comprising olefinsand saturates which process comprises the steps of: a. contacting saidmixture with an adsorbent at adsorption conditions to effect theselective adsorption of said olefins; b. withdrawing from the adsorbentstream comprising less selectively adsorbed feed mixture components; c.contacting the adsorbent with a desorbent material at desorptionconditions to effect desorption of olefins from the adsorbent; and, d.withdrawing from the adsorbent a stream containing feed mixture olefinsand desorbent; wherein said adsorbent is prepared by the steps of: i.contacting a base material cOmprising type X or type Y zeolite with afluoride-containing aqueous sodium hydroxide solution at ion exchangeconditions to effect the addition of sodium cations and the extractionof alumina from said base material; ii. washing the sodium-exchangedbase material at washing conditions until essentially free of sodiumhydroxide; and, iii. drying the material at conditions to reduce the LOIat 900* C. to less than about 10 wt. percent.
 5. The process of claim 4further characterized in that said adsorption and desorption conditionsare selected from a temperature within the range of from about 70* F. toabout 450* F. and a pressure within the range of from about atmosphericto about 500 psig. to maintain a liquid phase.
 6. The process of claim 4further characterized in that said olefins have from about 4 to about 25carbon atoms per molecule.